1. Field of the Invention
The present invention relates to an image forming apparatus for forming an image on a sheet.
2. Description of the Related Art
Conventionally, an image forming apparatus such as a copying machine and a printer for forming a toner image on a sheet by using an electrophotographic process includes a heat fixing device configured to fix, onto the sheet, an unfixed toner image formed on the sheet by heating and fixing the sheet and the toner image. Meanwhile, the sheet contains moisture. Therefore, when the sheet is heated by the fixing device, the moisture contained in the sheet vaporizes and adheres to a guide member, which adjoins the fixing device on the downstream side of the fixing device to guide the sheet. Such moisture may be condensed and result in a water droplet.
When the water droplet due to the moisture condensation adheres to the sheet passing through the guide member, particularly in a case where images are formed on both sides of the sheet, electric charges are not sufficiently applied to the sheet, and text blanking (blank area) occurs, which causes degradation of image quality. Further, when the water droplet adheres to the sheet, the sheet sticks to the guide member to cause a sheet jam.
Therefore, Japanese Patent Application Laid-Open No. 2007-187821 discloses a guide chute which causes less moisture condensation. The guide chute includes wire-shaped members coated with a resin, extending along a sheet conveying direction, and having a cornerless, convex cross-sectional shape on a sheet conveying path side, and holders having the wire-shaped members arranged on a plane along the sheet conveying path while the wire-shaped members are spaced apart from one another with a space. The wire-shaped member is formed by coating a metal with a resin. By the way, the image forming apparatus is becoming downsized nowadays, and the guide chute is also required to be downsized. Further, in the vicinity of the downstream side of the fixing device in the sheet conveying direction, there are provided a guide plate having added thereto a function of separating the sheet from the fixing device, and a conveyance roller for preventing the sheet jam, sheet corner folding, and sheet curling. Therefore, the installation space for the guide chute is narrow, and hence the demand for downsizing the guide chute is increasing much more.
The guide chute disclosed in Japanese Patent Application Laid-Open No. 2007-187821 is formed by welding the wire-shaped members to the holders. However, it is necessary to downsize the wire-shaped members and the holders for downsizing the guide chute. Thus, it is difficult to weld the wire members to the holders, which requires labor and time for the manufacturing.
Further, the wire-shaped member disclosed in Japanese Patent Application Laid-Open No. 2007-187821 is formed by coating a metal cored wire with a resin, and hence the cored wire needs to be coated with the resin after the cored wire is welded to the holder. Otherwise, the resin may be melted by heat of the welding. However, when the cored wire is coated with the resin after the welding, it is difficult to keep the coating thickness uniform, which may result in an uneven surface. Accordingly, in the conventional wire-shaped member, the leading edge of the sheet conveyed through the fixing device is engaged with the uneven surface of the wire-shaped member, which may cause the sheet jam.
Further, an image forming apparatus including the guide chute which is likely to cause the sheet jam has the following problem inherent therein. That is, the image forming apparatus needs to form an image on the sheet again as many times as the sheet jam has occurred.